Princess Maria Luisa of Savoy (1729–1767) points because she wants everyone to notice her pet.

A hallmark of human beings is the ability to use language. No other species of animal has language, although other species are capable of understanding and communicating quite a few things. Yet (non-human) animal communications cannot properly be called language. A closer look at human language and animal communication, and at the function language serves for us reveals important things about the human mind and about what it is to be human.

Both animals and humans use signs. A sign points to something other than itself. For example, when you point with your finger at a tree, you are making a sign. You want people to look at the tree, not at your finger. A lion’s roar (to scare off an intruder) is also a sign. It’s a warning sign for the intruder, not just noise the animal happens to be making. A bird’s song to attract a mate or establish territory is a sign in the same way. So is a written or spoken word. Both animals and humans use signs.

There are (for our purposes) two kinds of signs—signals and designators. A signal is a concrete sign that has a physical relationship with the object it signifies. Pointing at a tree is a signal (direction). Making a noise to ward off an intruder is a signal (warning). It is the concreteness that characterizes the communication as a signal. A signal points to or represents, in a physical way, what it signifies. That can include aiming (with a gesture) and implying (by a frightening noise). Other signals might include imitation (for example, saying “meow” to a cat, to indicate friendliness by sounding like a cat). Both animals and humans use signals. A paw or hand motion, a grunt, a shout or a roar, are all signals. Signals can be quite complex—consider the complex songs of birds or the dance of insects in a hive.

A designator, however, is a kind of sign that differs in a very important way from a signal. A designator points to an object, but it does so abstractly, not concretely. The spoken or written word “cat” has nothing physically to do with a cat. Unlike a gesture (pointing to a cat) or making the sound “meow”, the letters C-A-T feature nothing that concretely links the word to the animal. You only know what “cat” designates if you understand the word as used in English. By contrast, you could understand a signal like pointing to a cat or saying “meow” even if you spoke no English. Designators differ from signals in that they point to objects—things or concepts—abstractly.

Language is the systematic use of designators—the rule-based use of abstract signs. That is why a lion’s roar, an ape’s gesture, or a bird’s song are not really language. They are signals. A signal is not rule-based (signals have no grammar) and signals are concrete, not abstract.

Only humans have language because only humans are capable of rule-based abstract signing. Animals can often employ complex signals but no animal uses rule-based designators. Animals that can be trained to communicate using “language” (such as parrots or apes) are using words as signals, not as designators. For example, you can train your dog to go fetch the leash when you say “Do you want to go for a walk?” because he has learned to fetch the leash in response to those sounds, which he hears as a signal. He does not understand them as a grammatical construction and will certainly not go on to discuss the weather forecast with you. His communication is concrete, not abstract.

This raises a fascinating question: What is the purpose of language? Why does man, and no other animal, use language in addition to signals? As linguist Noam Chomsky has pointed out, the purpose of language is not essentially to communicate. Signals work well for communication. Language permits more complex communication under some circumstances but some signals are quite complex and serve to facilitate communication quite well. Sign language, which is mostly a system of signals, is a quite effective means of communication, even of conveying abstractions, but it is not (except when it signs the alphabet) language. It is derived from language.

The purpose of language is not primarily to communicate. The purpose of language is to enable man to think in a human way. Man alone is capable of abstract thought—thought about concepts that are universals, and not particular things. Man thinks about justice, and about mercy, about politics and imaginary numbers, and about countless concepts that are not particular physical things. This is abstract thought, and only humans think abstractly.

Animals are limited to thought about particulars. Dogs think about the food in their bowl. Humans think about nutrition. Dogs think about the good feeling they get when they are petted. Humans think about joy and love in an abstract sense. Both humans and animals have the capacity to think about particulars. Only humans also have the capacity to think about abstract concepts.

Every thought is about something. All thought is intentional, in the technical philosophical sense that it points to something. Thoughts about particular things—physical objects in the environment, imagination, or memory—are akin to signals.

But humans cannot think abstractly using signals. A signal points to a physical thing—a physical (or imagined or remembered) object. An abstract concept, such as mercy or justice, is not a physical thing. In order to think abstractly, we must use abstract signs—designators—to point to the conceptual objects of our thoughts. Consider: How could we contemplate mercy if we did not have the word “mercy,” if our thoughts were restricted to concrete objects (akin to signals)? We could imagine situations, persons, or objects that might be associated with mercy but we couldn’t contemplate mercy itself unless we had a word for it. Mercy isn’t a physical thing we can point to.

Language, which is the rule-based use of abstract designators, is essential for abstract thought because only designators can point to things that have no concrete physical existence. Only human beings think abstractly, and language is what makes abstract thought possible.

Note: Considerable publicity attends claims that great apes, kept as research subjects, have learned human language mastery, via American Sign Language for the Deaf. But the skepticism surrounding these stories is well justified according to observers such as Molly Roberts, “We wanted to believe in Koko, and so we did” (Chicago Tribune June 25, 2018) and Jane C. Hu, “What Do Talking Apes Really Tell Us?” (Slate, August 20, 2014). According to those who are not associated with the projects, human needs and expectations strongly colored interpretations of the interactions.

Michael Egnor is a neurosurgeon, professor of Neurological Surgery and Pediatrics and Director of Pediatric Neurosurgery, Neurological Surgery, Stonybrook School of Medicine

Also: by Michael Egnor: Does Brain Stimulation Research Challenge Free Will? If we can be forced to want something, is the will still free?

and

Is free will a dangerous myth?